Valorization of face masks produced during COVID-19 pandemic through hydrothermal carbonization (HTC): a preliminary study

Authors: FARRU, GIANLUIGI - University Of Cagliari; LIBRA, JUDY - Leibniz Institute; Ro, Kyoung; CANNAS, CARLA - University Of Cagliari; CARA, CLAUDIO - University Of Cagliari; MUNTONI, A - University Of Cagliari; PIREDDA, M - University Of Cagliari; CAPPAI, GIOVANNA - University Of Cagliari

Submitted to: Sustainability
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2023
Publication Date: 6/10/2023
Citation: Farru, G., Libra, J., Ro, K.S., Cannas, C., Cara, C., Muntoni, A., Piredda, M., Cappai, G. 2023. Valorization of face masks produced during COVID-19 pandemic through hydrothermal carbonization (HTC): a preliminary study. Sustainability. 15(12):9382. https://doi.org/10.3390/su15129382.
DOI: https://doi.org/10.3390/su15129382

Interpretive Summary: Recently, the use of disposable face masks has been mandated in most world regions to prevent and control the spread of the Covid-19 pandemic. This led to a sudden increase in large volumes of potentially infectious waste face mask material that must be safely managed and disposed of. In this preliminary study, hydrothermal carbonization (HTC) was evaluated as a potential method of converting surgical mask waste into value-added carbonaceous material for use as a fuel or in various agro-environmental applications. Hydrothermal carbonization (HTC) uses water as the reaction medium to convert wet organic residues to carbon-rich solid and liquid products. The HTC treatment transformed the spent masks into an amorphous solid with reduced in mass and volume. The carbon content and the calorific value of the produced hydrochars were higher than that of the original masks. When the HTC experiment was carried out with acetic acid, a new crystal phase was produced, which was identified as terephthalic acid. Our results suggested that the spent masks could be treated through HTC for potentially achieving not only sanitization and volume reduction but also producing a solid fuel or a raw material for terephthalic acid production, a precursor in surgical mask production.

Technical Abstract: Recently, the use of disposable face masks has been mandated in most world regions to prevent and control the spread of the Covid-19 pandemic. This led to a sudden increase in large volumes of potentially infectious waste face mask material that must be safely managed and disposed of. Innovative and sustainable approaches are called for converting used face masks into useful end products to attain a circular economy. In this preliminary study, hydrothermal carbonization (HTC) was evaluated as a potential method of converting surgical mask waste into value-added carbonaceous material for use as a fuel or in various agro-environmental applications. HTC treatments were carried out at 220 degree Celsius (°C) and a holding time of 3 hours in presence or absence of acetic acid. Physico-chemical and thermal characteristics of the produced hydrochar were evaluated using thermogravimetric analysis (TGA), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR), and nitrogen gas (N2)- physisorption analyzers. Under the applied conditions, masks formed an amorphous solid with reduced in mass and volume. The carbon content and the calorific value of the produced hydrochars were higher than that of the original masks. When the HTC experiment was carried out with acetic acid, a new crystal phase was produced, which was identified as terephthalic acid. Our results suggested that surgical masks, made of non-renewable and non-biodegradable polymers, could be treated through hydrothermal carbonization for potentially achieving not only sanitization and volume reduction but also producing a solid fuel or a raw material for terephthalic acid production, a precursor in surgical mask production.